Inhibition of depolarization-induced [ 3H]noradrenaline release from SH-SY5Y human neuroblastoma cells by some second-generation H 1 receptor antagonists through blockade of store-operated Ca 2+ channels (SOCs)

Abstract

In the present study, the effect of the blockade of membrane calcium channels activated by intracellular Ca 2+ store depletion on basal and depolarization-induced [ 3H]norepinephrine ([ 3H]NE) release from SH-SY5Y human neuroblastoma cells was examined. The second-generation H 1 receptor blockers astemizole, terfenadine, and loratadine, as well as the first-generation compound hydroxyzine, inhibited [ 3H]NE release induced by high extracellular K + concentration ([K +] e) depolarization in a concentration-dependent manner (the ic 50s were 2.3, 1.7, 4.8, and 9.4 μM, respectively). In contrast, the more hydrophilic second-generation H 1 receptor blocker cetirizine was completely ineffective (0.1–30 μM). The inhibition of high [K +] e-induced [ 3H]NE release by H 1 receptor blockers seems to be related to their ability to inhibit Ca 2+ channels activated by Ca i 2+ store depletion (SOCs). In fact, astemizole, terfenadine, loratadine, and hydroxyzine, but not cetirizine, displayed a dose-dependent inhibitory action on the increase in intracellular Ca 2+ concentrations ([Ca 2+] i) obtained with extracellular Ca 2+ reintroduction after Ca i 2+ store depletion with thapsigargin (1 μM), an inhibitor of the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA) pump. The rank order of potency for SOC inhibition by these compounds closely correlated with their inhibitory properties on depolarization-induced [ 3H]NE release from SH-SY5Y human neuroblastoma cells. Nimodipine (1 μM) plus ω-conotoxin (100 nM) did not interfere with the present model for SOC activation. In addition, the inhibition of depolarization-induced [ 3H]NE release does not seem to be attributable to the blockade of the K + currents carried by the K + channels encoded by the human Ether-a-Gogo Related Gene (I HERG) by these antihistamines. In fact, whole-cell voltage-clamp experiments revealed that the ic 50 for astemizole-induced hERG blockade is about 300-fold lower than that for the inhibition of high K +-induced [ 3H]NE release. Furthermore, current-clamp experiments in SH-SY5Y cells showed that concentrations of astemizole (3 μM) which were effective in preventing depolarization-induced [ 3H]NE release were unable to interfere with the cell membrane potential under depolarizing conditions (100 mM [K +] e), suggesting that hERG K + channels do not contribute to membrane potential control during exposure to elevated [K +] e. Collectively, the results of the present study suggest that, in SH-SY5Y human neuroblastoma cells, the inhibition of SOCs by some second-generation antihistamines can prevent depolarization-induced neurotransmitter release.